The onset of densification of cellular solids represents the start of the cell wall interactions, which enhance the compressive resistance of a cellular solid. Currently, there exists ambiguity in the definition and uncertainty in the determination of the compressive strain, from which the densification regime starts. The onset strain of densification and the densification strain are defined and distinguished in the present study. Several commonly used methods to determine the onset strain of densification are examined. It is shown that the method based on the energy absorption efficiency curve gives unique and consistent results. Two types of energy absorption efficiency curves are identified. Further justifications of the use of the energy absorption efficiency method are provided for various types of cellular solids.

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Summary. -The aim of this paper is threefold. First, to describe the general evolution of bonding and bridging social capital in Jordan. Second, to explore the role of state policies in affecting the various forms of social capital. Finally, to analyze how poverty and economic reform influence the extent and nature of social capital. Social networks, a crucial element of social capital, and cleavages are strongly affected by political and economic dislocations. The former include wars and civil wars, while the latter include state policies and economic conditions. Thus wasta, an old but still significant form of social capital in the Arab World, becomes helpful in good times but destructive in bad times. Successful economic reform requires a good understanding of the nature of social relations and of the ways in which social networks themselves are used by members during good times and bad times for both survival and advancement.

The dynamic compressive characteristics of a closed cell aluminium alloy foam (manufactured by Hydro Aluminium AS, Norway) have been studied experimentally by using a direct impact technique for a range of velocities up to 210 m s 1 . Experimental data on the dynamic initial crushing and plateau stresses are compared for two average cell sizes of approximately 4 and 14 mm. The data reveal signi® cant dynamic enhancements of the initial crushing strengths throughout the range of velocities used. The dynamic plateau stresses are insensitive to impact velocity below the values of 50 and 100 m s 1 for the large and small cell foams respectively. Beyond a critical velocity value of ~100 m s 1 , the crushing wave front propagates through the foam with shock like characteristics. The inertia effects associated with the dynamic localisation of crushing and the microinertia of the cell wall/edge material on the dynamic strength enhancement are discussed. A one-dimensional shock model based on a rate independent, rigid, perfectly plastic locking idealisation of the nominal stress ± strain curve for foams is employed to provide a ® rst order understanding of the various parameters involved in the crushing process. The results of the analyses are seen to predict well the dynamic strength enhancements that are measured experimentally. The sources of discrepancies are highlighted and discussed, as are the limitations and shortcomings of the shock model.MST/5396

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